Theoretical and experimental studies on concerted elimination of 1,
2-bromochloroethane monocation to C2H4+ and BrCl
Abstract
We calculate the concerted pathway of 1, 2-bromochloroethane monocation
to C2H4+ and BrCl using the Minnesota density functional M06-2X and the
def2-TZVP basis set. We also calculate the elimination channel of 1,
2-bromochloroethane monocation to C2H4 and BrCl+ for the reason that
positive charge can be assigned to either moiety in the fragmentation
process of 1,2-C2H4BrCl+. Our results demonstrate that the elimination
channel of 1, 2-bromochloroethane monocation to C2H4+ and BrCl is
preferred, and the singly charged 1,2-bromochloroethane ions surpass two
energy barriers and then separate into C2H4+ + BrCl by an asynchronous
concerted process. Experimentally, we confirm that this elimination
channel is from the dissociative ionization process of
1,2-bromochloroethane monocation by dc-slice imaging technique. Besides,
we can see in laser-induced time-of-flight mass spectra of
1,2-bromochloroethane that fragment ion C2H4+ occur at the laser
intensity of 6.0×1013 W/cm2 while BrCl+ occur at a higher laser
intensity, which is consistent with the theoretical results that
appearance energy of ion C2H4+ should be lower than that of BrCl+, and
this is the reason why the low-velocity component of ion BrCl+ is absent
from our sliced images.